The invention relates to the field of microwave band antennae and can be used in designing antennae for small-size mobile radar antiaircraft-rocket systems for acquisition and tracking of targets and rockets as well as in microwave antenna equipment designed for other purposes.
It is known that such a system arranged, in the majority of cases, to be disposed on a single transport vehicle (a self-propelled chassis) must enable to scan the area in a target search, followed by tracking the targets thus acquired, that is, periodically determining the three coordinates of the targets in space and lashing the target motion lanes in order to make a decision to destroy a target. After rockets are fired out to destroy the targets, the system must ensure their lock-on and guidance at the targets thus being tracked down to the moment of their destruction. The necessity to solve these problems while arranging equipment on a single self-propelled chassis leads to imposing substantially higher requirements on an antenna-feeder system of such a radar station, many of these requirements being conflicting. Thus, for instance, in order to improve the radar resolution and improve accuracy in determining the angular coordinates of a target, it is necessary to form a sufficiently narrow directional radiation pattern of the antenna, but for scanning the area and locking on a rocket, the directional radiation pattern of the antenna must be wide enough. The antenna must ensure a high capacity of the radar station for simultaneous operation with several targets and rockets as well as adaptability to various widths of its directional radiation patternxe2x80x94for this purpose, the antenna must have a high speed of response when the directional radiation pattern thereof is moving in space and its width is changing. At the same time, the antenna for the radar station of a small-size mobile antiaircraft-rocket system must have small overall dimensions and mass and low costxe2x80x94factors which are frequently decisive in selecting the type of antennae.
The aforementioned requirements to an antenna for the radar station of a small-size antiaircraft-rocket system would be met to the largest extent by antennae of a phased array type with electronic scanning of their directional radiation patterns. Known in the art are antiaircraft-rocket systems which use antennae of the phased array typexe2x80x94for instance, a multi-functional radar station of the xe2x80x9cPATRIOTxe2x80x9d antiaircraft-rocket system, a radar station of the xe2x80x9cAEGISxe2x80x9d shipboard antiaircraft-rocket system. However, the constructional features of phased antenna arrays as realized in providing antennae for the above-mentioned radar stations appear to be unacceptable when developing small-size target and rocket acquisition and tracking radar stations arranged to be disposed on a single self-propelled chassis, in connection with their rather high complexity, large overall dimensions and mass, and a high cost. This explains the fact that use is made of reflector-type antennae with electromechanical scanning of beam until recently in the known radar stations of small-size target and rocket acquisition and tracking systems. Such antennae are used in xe2x80x9cCrotalxe2x80x9d (France), xe2x80x9cRolandxe2x80x9d (France, Germany) and xe2x80x9cOsaxe2x80x9d (Russia) systems.
It is a reflector-type antenna for a target radar of the xe2x80x9cOsaxe2x80x9d antiaircraft-rocket system (see Technical Description of Combat Vehicle of Antiaircraft Rocket System xe2x80x9cOsa-AKMxe2x80x9d, GP IEMZ, Ishevsk, 1980) that is taken to be the most relevant prior art prototype.
The antenna for that system comprises a radiating aperture (surface) and a microwave section. The radiating aperture is formed by a parabolic reflector of polarization-rotating type with a reflector-filter. The antenna surface is excited by means of a feed. The microwave section which comprises a system of E-H tees, a modulator, a slot bridge hybrid, a circulator, connects a radiator to a transmitter and a receiver of the radar station. Scanning of the directional radiation patterns within a predetermined angular sector is effected in azimuth and elevation planes by means of an electromechanical rotating device which comprises azimuth and elevation drives.
While meeting the requirements of simplicity, small overall dimensions and mass, and low cost as imposed on an antenna for the radar station of a mobile system, the antennae of the most relevant prior art prototype and analogues possess, when used with modern strike weapons, a number of substantial shortcomings which include:
long target acquisition and lock-on time, with the directional radiation pattern of the antenna being mechanically moved in space;
impossibility to track simultaneously several targets and rockets because of their high speeds;
lack of swift adaptation to various widths of the directional radiation pattern of the antenna;
high level of antenna side lobes because of shadowing the working surface of the reflector by the feed and by the design members of both the feed and the reflector-filter, with a resulting deterioration of noise immunity of the radar station.
It is an object of the invention to provide a relatively cheap antenna with electronic scanning of its directional radiation patterns within a sector of angles as required for radar stations of small-size antiaircraft-rocket systems so that it will be free from the aforementioned shortcomings of the prototype antenna. Along with this, the antenna characteristics of the prototype must be improved, with the requirements being met which are imposed on the cost, mass, overall dimensions and allowable power consumption and which are dictated by the requirements to a small-size mobile radar station.
A further object of the invention is to provide an antenna having a small number of controllable elements and which ensures electronic scanning of its directional radiation patterns within a limited sector of angles dictated by the requirements to radar stations of the above-mentioned systems, with the time needed to move the directional radiation pattern to any point of the scanning sector being no longer than fractions of a millisecond.
The antenna must form summation-difference directional radiation patterns for a monopulse method of target direction finding, must be adaptable to various widths of the directional radiation patterns and have a gain not less than that of the prototype but a lower level of side radiation in the summation directional radiation pattern. The antenna must have overall dimensions and mass to meet the requirements of disposing it in small-size radar stations. Since the cost is of importance for army radar stations, the above-mentioned properties of the antenna must be obtained with its minimum cost.
These objects of the invention are accomplished owing to the fact that the radiating aperture of the antenna is made in the form of four subarrays of the same type, each of which is provided with a feed system, a phasing system with a small number of controllable phase shifters, and a radiation system comprising radiators having a special (table-like) shape of the directional radiation pattern, all the subarrays being provided with a common beam control system. Along with this, each radiator of the radiation system is connected to a respective electrically controlled phase shifter of the phasing system, which shifter is connected to one of the outputs of the feed system. The feed systems are made in the form of parallel or series microwave transmission lines and have one input for each subarray and so many outputs as there are controllable phase shifters. The inputs of the feed system are connected via a system of four E-H tees, three of which are folded in the E-plane, and a circulator by microwave lines to the transmitter and receiver of the radar station. The control inputs of the electrically controlled phase shifters are connected to the outputs of the beam control system. The radiating aperture of the antenna is mounted together with all of its components on the system""s chassis platform having both azimuth and elevation electromechanical drives.
In order to ensure adaptation to various widths of the directional radiation patterns, the antenna is provided with a unit for generating phase distribution corrections. For mutual phasing of the subarrays, the antenna is provided with a source of a monitoring signal.
The concept of the invention consists in constructing a phased antenna array which meets all the above-mentioned requirements with a small number of controllable elements (phase shifters), owing to that radiating elements are provided which have special directional radiation patterns. The disclosed invention allows to provide a phased antenna array having a number of controllable elements which is several times smaller than that of the known equidistant phased antenna arrays having the same width of their directional radiation patterns and in which used are the radiators similar to those used in the above-mentioned xe2x80x9cPATRIOTxe2x80x9d and xe2x80x9cAEGISxe2x80x9d antiaircraft-rocket systems and in the majority of other radar stations with phased antenna arrays.
The disclosed equidistant phased antenna array has a distance between the controllable elements equal to several wavelengths, whereas similar phased antenna arrays have a distance between their elements less than one wavelength.